<script>
    function Foo() {
        Foo.a = function () {
            console.log(1)
        }
        this.a = function () {
            console.log(2)
        }
    }
    Foo.prototype.a = function () {
        console.log(3)
    }
    Foo.a = function () {
        console.log(4)
    }
    Foo.a();//4
    let obj = new Foo();
    obj.a();//2
    Foo.a();//1

</script>